They actually do that on RCCL. It has actually been something that speeds up the process. The lifejacket has cabin # and they know by clipboard the # of people in the cabin. When they are near the end and some cabin #'s and people aren't accounted for, crew finds them and we all give them the evil eye (others the one finger salute). They are really efficient. There's always someone who feels it doesn't apply to them.